/* inftrees.c -- generate Huffman trees for efficient decoding
 * Copyright (C) 1995-2003 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zutil.h"
#include "inftrees.h"

#define MAXBITS 15

/*
Build a set of tables to decode the provided canonical Huffman code.
The code lengths are lens[0..codes-1].  The result starts at *table,
whose indices are 0..2^bits-1.  work is a writable array of at least
lens shorts, which is used as a work area.  type is the type of code
to be generated, CODES, LENS, or DISTS.  On return, zero is success,
-1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
on return points to the next available entry's address.  bits is the
requested root table index bits, and on return it is the actual root
table index bits.  It will differ if the request is greater than the
longest code or if it is less than the shortest code.
 */

int inflate_table(codetype type, WORD *lens, DWORD codes, code **table, DWORD *bits, WORD *work)
{
  DWORD len; /* a code's length in bits */
  DWORD sym; /* index of code symbols */
  DWORD min, max; /* minimum and maximum code lengths */
  DWORD root; /* number of index bits for root table */
  DWORD curr; /* number of index bits for current table */
  DWORD drop; /* code bits to drop for sub-table */
  int left; /* number of prefix codes available */
  DWORD used; /* code entries in table used */
  DWORD huff; /* Huffman code */
  DWORD incr; /* for incrementing code, index */
  DWORD fill; /* index for replicating entries */
  DWORD low; /* low bits for current root entry */
  DWORD mask; /* mask for low root bits */
  code this; /* table entry for duplication */
  code *next; /* next available space in table */
  const WORD *base; /* base value table to use */
  const WORD *extra; /* extra bits table to use */
  int end; /* use base and extra for symbol > end */
  WORD count[MAXBITS + 1]; /* number of codes of each length */
  WORD offs[MAXBITS + 1]; /* offsets in table for each length */

  static const WORD lbase[31] =
  {
    3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0
  }; /* Length codes 257..285 base */
  static const WORD lext[31] =
  {
    16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 76, 66
  }; /* Length codes 257..285 extra */
  static const WORD dbase[32] =
  {
    1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577, 0, 0
  }; /* Distance codes 0..29 base */
  static const WORD dext[32] =
  {
    16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29, 64, 64
  }; /* Distance codes 0..29 extra */


  /*
  Process a set of code lengths to create a canonical Huffman code.  The
  code lengths are lens[0..codes-1].  Each length corresponds to the
  symbols 0..codes-1.  The Huffman code is generated by first sorting the
  symbols by length from short to long, and retaining the symbol order
  for codes with equal lengths.  Then the code starts with all zero bits
  for the first code of the shortest length, and the codes are integer
  increments for the same length, and zeros are appended as the length
  increases.  For the deflate format, these bits are stored backwards
  from their more natural integer increment ordering, and so when the
  decoding tables are built in the large loop below, the integer codes
  are incremented backwards.

  This routine assumes, but does not check, that all of the entries in
  lens[] are in the range 0..MAXBITS.  The caller must assure this.
  1..MAXBITS is interpreted as that code length.  zero means that that
  symbol does not occur in this code.

  The codes are sorted by computing a count of codes for each length,
  creating from that a table of starting indices for each length in the
  sorted table, and then entering the symbols in order in the sorted
  table.  The sorted table is work[], with that space being provided by
  the caller.

  The length counts are used for other purposes as well, i.e. finding
  the minimum and maximum length codes, determining if there are any
  codes at all, checking for a valid set of lengths, and looking ahead
  at length counts to determine sub-table sizes when building the
  decoding tables.
   */

  /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */

  for (len = 0; len <= MAXBITS; len++)
  {
    count[len] = 0;
  }

  for (sym = 0; sym < codes; sym++)
  {
    count[lens[sym]]++;
  }

  /* bound code lengths, force root to be within code lengths */

  root =  *bits;

  for (max = MAXBITS; max >= 1; max--)
  {
    if (count[max] != 0)
    {
      break;
    }
  }

  if (root > max)
  {
    root = max;
  }

  if (max == 0)
  {
    return  - 1;
  }

  /* no codes! */

  for (min = 1; min <= MAXBITS; min++)
  {
    if (count[min] != 0)
    {
      break;
    }
  }

  if (root < min)
  {
    root = min;
  }

  /* check for an over-subscribed or incomplete set of lengths */

  left = 1;

  for (len = 1; len <= MAXBITS; len++)
  {
    left <<= 1;
    left -= count[len];

    if (left < 0)
    {
      return  - 1;
    }
    /* over-subscribed */
  }

  if (left > 0 && (type == CODES || (codes - count[0] != 1)))
  {
    return  - 1;
  }
  /* incomplete set */

  /* generate offsets into symbol table for each length for sorting */

  offs[1] = 0;

  for (len = 1; len < MAXBITS; len++)
  {
    offs[len + 1] = offs[len] + count[len];
  }

  /* sort symbols by length, by symbol order within each length */

  for (sym = 0; sym < codes; sym++)
  {
    if (lens[sym] != 0)
    {
      work[offs[lens[sym]]++] = (WORD)sym;
    }
  }

  /*
  Create and fill in decoding tables.  In this loop, the table being
  filled is at next and has curr index bits.  The code being used is huff
  with length len.  That code is converted to an index by dropping drop
  bits off of the bottom.  For codes where len is less than drop + curr,
  those top drop + curr - len bits are incremented through all values to
  fill the table with replicated entries.

  root is the number of index bits for the root table.  When len exceeds
  root, sub-tables are created pointed to by the root entry with an index
  of the low root bits of huff.  This is saved in low to check for when a
  new sub-table should be started.  drop is zero when the root table is
  being filled, and drop is root when sub-tables are being filled.

  When a new sub-table is needed, it is necessary to look ahead in the
  code lengths to determine what size sub-table is needed.  The length
  counts are used for this, and so count[] is decremented as codes are
  entered in the tables.

  used keeps track of how many table entries have been allocated from the
  provided *table space.  It is checked when a LENS table is being made
  against the space in *table, ENOUGH, minus the maximum space needed by
  the worst case distance code, MAXD.  This should never happen, but the
  sufficiency of ENOUGH has not been proven exhaustively, hence the check.
  This assumes that when type == LENS, bits == 9.

  sym increments through all symbols, and the loop terminates when
  all codes of length max, i.e. all codes, have been processed.  This
  routine permits incomplete codes, so another loop after this one fills
  in the rest of the decoding tables with invalid code markers.
   */

  /* set up for code type */

  switch (type)
  {
    case CODES:
      base = extra = work; /* dummy value--not used */
      end = 19;
      break;

    case LENS:
      base = lbase;
      base -= 257;
      extra = lext;
      extra -= 257;
      end = 256;
      break;

      default:  /* DISTS */
      base = dbase;
      extra = dext;
      end =  - 1;
  }

  /* initialize state for loop */

  huff = 0; /* starting code */
  sym = 0; /* starting code symbol */
  len = min; /* starting code length */
  next =  *table; /* current table to fill in */
  curr = root; /* current table index bits */
  drop = 0; /* current bits to drop from code for index */
  low = (DWORD)( - 1); /* trigger new sub-table when len > root */
  used = 1 << root; /* use root table entries */
  mask = used - 1; /* mask for comparing low */

  /* check available table space */

  if (type == LENS && used >= ENOUGH - MAXD)
  {
    return 1;
  }

  /* process all codes and make table entries */

  for (;;)
  {
    /* create table entry */
    this.bits = (BYTE)(len - drop);
    if ((int)(work[sym]) < end)
    {
      this.op = (BYTE)0;
      this.val = work[sym];
    }
    else if ((int)(work[sym]) > end)
    {
      this.op = (BYTE)(extra[work[sym]]);
      this.val = base[work[sym]];
    }
    else
    {
      this.op = 96; /* end of block */
      this.val = 0;
    }

    /* replicate for those indices with low len bits equal to huff */
    incr = 1 << (len - drop);
    fill = 1 << curr;
    do
    {
      fill -= incr;
      next[(huff >> drop) + fill] = this;
    }
    while (fill != 0);

    /* backwards increment the len-bit code huff */
    incr = 1 << (len - 1)
      ;

    while (huff &incr)
    {
      incr >>= 1;
    }

    if (incr != 0)
    {
      huff &= incr - 1;
      huff += incr;
    }
    else
    {
      huff = 0;
    }

    /* go to next symbol, update count, len */
    sym++;

    if (--(count[len]) == 0)
    {
      if (len == max)
      {
        break;
      }
      len = lens[work[sym]];
    }

    /* create new sub-table if needed */
    if (len > root && (huff &mask) != low)
    {
      /* if first time, transition to sub-tables */
      if (drop == 0)
      {
        drop = root;
      }

      /* increment past last table */
      next += 1 << curr;

      /* determine length of next table */
      curr = len - drop;
      left = 1 << curr;

      while (curr + drop < max)
      {
        left -= count[curr + drop];

        if (left <= 0)
        {
          break;
        }
        curr++;
        left <<= 1;
      }

      /* check for enough space */
      used += 1 << curr;

      if (type == LENS && used >= ENOUGH - MAXD)
      {
        return 1;
      }

      /* point entry in root table to sub-table */
      low = huff &mask;

      (*table)[low].op = (BYTE)curr;
      (*table)[low].bits = (BYTE)root;
      (*table)[low].val = (WORD)(next -  *table);
    }
  }

  /*
  Fill in rest of table for incomplete codes.  This loop is similar to the
  loop above in incrementing huff for table indices.  It is assumed that
  len is equal to curr + drop, so there is no loop needed to increment
  through high index bits.  When the current sub-table is filled, the loop
  drops back to the root table to fill in any remaining entries there.
   */
  this.op = 64; /* invalid code marker */
  this.bits = (BYTE)(len - drop);
  this.val = (WORD)0;

  while (huff != 0)
  {
    /* when done with sub-table, drop back to root table */
    if (drop != 0 && (huff &mask) != low)
    {
      drop = 0;
      len = root;
      next =  *table;
      curr = root;
      this.bits = (unsigned char)len;
    }

    /* put invalid code marker in table */
    next[huff >> drop] = this;

    /* backwards increment the len-bit code huff */

    incr = 1 << (len - 1);
    while (huff &incr)
    {
      incr >>= 1;
    }

    if (incr != 0)
    {
      huff &= incr - 1;
      huff += incr;
    }
    else
    {
      huff = 0;
    }
  }

  /* set return parameters */
  *table += used;
  *bits = root;
  return 0;
}
